The present invention relates to a curable sheet to be used for the formation of a wiring circuit layer by the transfer from a transfer base material, and to a multilayer wiring board using a cured sheet as an insulating layer, which has been obtained by curing the above-described curable sheet, for example, a multilayer wiring board suitable for use as a semiconductor device package. The present invention also relates to a process for producing the above-described multilayer wiring board.
As a wiring board, for example, a multilayer wiring board used as a semiconductor device package, a multilayer printed wiring board produced by adhering a copper foil onto the surface of each of insulating substrates including a resin, etching the copper foil to form a minute circuit and then stacking the resulting substrates one on top of the other has been proposed conventionally and employed in practice. Recently, there is a demand for the development of a multilayer printed wiring board having a more precise and high-density circuit. The conventional multilayer printed wiring board however cannot satisfy such a demand because in such a wiring board, interlayer connection is attained by plating inside of a thorough-hole formed to penetrate through a substrate so that this through-hole imposes a limitation on circuit designing and makes it difficult to accomplish high-density interconnection. Recently developed with a view to satisfy such a demand is a so-called build-up process, wherein insulating layers and wiring circuit layers are alternately formed by coating of the insulating layer, plating or via-hole formation over a predetermined substrate surface to effect multilayer lamination.
In this build-up process, however, layers are formed not simultaneously but successively so that a yield of the finished product corresponds to the multiplication product of the yields of successively formed layers, making it essentially difficult to heighten the yield. In addition, a build-up substrate using a photosensitive resin is accompanied with the problem that introduction of a photosensitive group into the resin lowers heat resistance or water absorption resistance of the substrate, which makes it impossible to satisfy the performances required for it in near future as a semiconductor device package.
In recent years, a thermosetting polyphenylene ether resin having high heat resistance and excellent water absorption resistance has drawn attentions and its application to a multilayer printed wiring board has been tried.
An object of the present invention is to provide a curable sheet for circuit transfer which comprises a thermosetting polyphenylene ether resin composition, permits formation of a precise and high-density circuit with a high productivity, and is excellent in heat resistance and water absorption resistance; and moreover to provide a curable sheet which can be used for a multilayer wiring board having long term stability under a high temperature shelf test at 130xc2x0 C. or higher.
Another object of-the present invention is to provide a multilayer wiring board produced using the above-described curable sheet.
A further other object of the present invention is to provide a process for producing the above-described multilayer wiring board.
Other objects and effects of the invention will become more apparent from the following description.
As a result of the extensive investigation on the above-described objects, the present inventors found that by transferring a wiring circuit to a curable sheet for circuit transfer, which contains a thermosetting polyphenylene ether resin composition having a specific composition, from a transfer base material, curable insulating layers stacked one after another can be cured in one step, leading to simplification of the multiplayer lamination, and that the conductor resistance varies largely not only by the penetration of oxygen or moisture from the outer circumstances, which has so far been considered as its cause, but also by impurities contained in a brominated flame retardant, thus leading to the completion of the invention.
The above-described objects of the invention have therefore been achieved by providing the following curable sheets, multilayer wiring boards and processes for producing a multilayer wiring board.
1. A curable sheet for the formation of a wiring circuit layer by circuit transfer from a transfer base material, which sheet comprises a thermosetting polyphenylene ether resin composition comprising:
(A) a reaction product between a polyphenylene ether resin and an unsaturated carboxylic acid or acid anhydride;
(B) triallyl isocyanurate and/or triallyl cyanurate;
(C) a hydrogenated block copolymer obtained by hydrogenation of a block copolymer having at least one polymer block A mainly comprising an aromatic vinyl compound and at least one polymer block B mainly comprising a conjugated diene compound; and
(D) an inorganic filler,
said composition containing 45 to 55 parts by weight of Component (A), 55 to 45 parts by weight of Component (B) and 25 to 35 parts by weight of Component (C), each based on 100 parts by weight of the total of Components (A) and (B), and containing 20 to 80 vol. % of Component (D).
2. The curable sheet according to the above item 1, wherein the thermosetting polyphenylene ether resin composition further comprises (E) a brominated flame retardant in an amount of 10 to 30 parts by weight based on 100 parts by weight of the total of Components (A) and (B) and the brominated flame retardant (E) contains, as impurities, sodium bromide (NaBr) and bromine (Br2) at a weight ratio of 50 ppm or less and 100 ppm or less, respectively.
3. A multilayer wiring board comprising a resin-containing insulating layer and a wiring circuit layer disposed on the surface and/or inside of the insulating layer,
wherein said insulating layer is obtained by curing a curable sheet according to the above item 1 or 2 and at least a part of the wiring circuit layer is formed by transfer from a transfer base material having thereon a wiring circuit layer comprising a metal foil.
4. The multilayer wiring board according to the above item 3, which further comprises a via-hole conductor for electrically connecting adjacent wiring circuit layers,
wherein the via-hole conductor is formed by filling a conductive paste in a through-hole, and
wherein a wiring circuit layer comprising a metal foil having a thickness of at least 0.05 time the thickness of the insulating layer is embedded in the insulating layer.
5. The multilayer wiring board according to the above item 3, which has, inside thereof, an inner layer comprising: a cured composite material layer obtained by impregnating reinforced fibers with a polyphenylene ether resin composition comprising (A) a reaction product between a polyphenylene ether resin, and an unsaturated carboxylic acid or acid anhydride and (B) triallyl isocyanurate and/or triallyl cyanurate, the contents of Components (A) and (B) being 45 to 55 parts by weight and 55 to 45 parts by weight, respectively, each based on 100 parts by weight of the total of Components (A) and (B); and a wiring circuit layer at least a part of which is formed by transfer from a transfer base material having thereon a wiring circuit layer comprising a metal foil.
6. The multilayer wiring board according to the above item 5, which further comprises a via-hole conductor for electrically connecting adjacent wiring circuit layers,
wherein said via-hole conductor is formed by filling a conductive paste in a through-hole, and
wherein a wiring circuit layer comprising a metal foil having a thickness of at least 0.05 time the thickness of the insulating layer is embedded in each of the insulating layer and cured complex material layer.
7. A process for producing a multilayer wiring board, which comprises:
(a) forming a wiring circuit layer on a surface of a transfer base material;
(b) forming a via-hole conductor by making a through-hole in a curable sheet according to the above item 1 or 2 and filling a conductive paste in the through-hole;
(c) stacking the resulting curable sheet, with the via-hole conductor formed therein, over the transfer base material having thereon the wiring circuit layer, and bonding them under pressure, thereby forming an insulating layer;
(d) releasing the transfer base material from the surface of the insulating layer obtained in step (c) and transferring the wiring circuit layer on the surface of the transfer base material to the surface of the insulating layer; and
(e) stacking a plurality of the insulating layers obtained through the steps (a) to (d) one after another and curing the resin simultaneously by heating and pressurizing means.
8. A process for producing a multilayer wiring board, which comprises: preparing an inner layer which comprises a curable composite material layer obtained by impregnating reinforced fibers with a polyphenylene ether resin composition comprising (A) a reaction product between a polyphenylene ether resin and an unsaturated carboxylic acid or acid anhydride and (B) triallyl isocyanurate and/or triallyl cyanurate, the contents of Components (A) and (B) being 45 to 55 parts by weight and 55 to 45 parts by weight, respectively, each based on 100 parts by weight of the total of Components (A) and (B), followed by drying, and a wiring circuit layer at least a part of which is formed by circuit transfer from a transfer base material having thereon a wiring circuit layer comprising a metal foil; stacking, over an outer surface of the inner layer, insulating layers which have a wiring circuit layer formed thereon and which is obtained through the steps (a) to (d) of the production process of a multilayer wiring board according to yjr above item 7; and curing the resin simultaneously.
The present invention is based on the finding that a plurality of curable insulating layers stacked one after another can be cured simultaneously by forming a wiring circuit layer on a curable sheet for circuit transfer, which comprises a thermosetting polyphenylene ether resin composition having a specific composition, by transferring thereto the wiring circuit layer from a transfer base material and this enables simplification of the lamination step. It has been understood that in order to produce a multilayer wiring board by this transfer process in a high yield, an insulating resin composition to be employed for it should have various properties as described below:
(1) adhesion for facilitating circuit transfer,
(2) melt properties for retaining the position of a circuit upon curing a substrate under pressure,
(3) handling properties of an uncured sheet, and
(4) processability for facilitating the processing of an electrically connecting through-hole.
Use of the curable sheet of the invention comprising a thermosetting polyphenylene ether resin composition having a specific composition makes it possible to provide a curable resin sheet which satisfies all of the adhesion, melt properties, handling properties and processability. Moreover, use of this curable resin sheet enables simultaneous stacking and curing of curable insulating layers, thereby simplifying the step for the formation of a multilayer structure.